"Four years before, as a cross-country runner at Colorado College, Krupicka had had a revelation. For much of his life he had been running in clunky, motion-stabilizing shoes with orthotic inserts, and for most of that time he had struggled with stress fractures in his legs.

"He wanted a shoe that would mimic the design of the human foot, which spreads out shock through the foot's arch and the runner's bent knees.

"'But there were none,' Krupicka said. 'I was so frustrated.'

"Every shoe he looked at, with the exception of racing flats, had a big fat heel getting in the way. And racing flats could not hold up on the trails.

"So one day he pulled out a kitchen knife and started hacking the heel of a pair of old New Balances. Over the next few months, between runs, he cut off more and more pieces he felt he did not need. He did the same to every new pair of shoes he bought.

"...'Since I started running in those shoes I haven't had a stress fracture,' Krupicka said. 'It encourages you to run in a much more natural way.'

"New Balance asked Krupicka to work with them on a new line of shoes. The company would come up with designs. He would test them on the trail, then, Gothie said, 'take the switchblade to them...'

"...Krupicka said that while he ignores most trends, he is pleased with this one.

"'It is a trend built on some actual fact and truth,' he said, because it encourages people to run in a more 'natural way.'..."